1. Field of the Invention
The present invention relates to an ophthalmic photographing apparatus used in opthalmologist's offices, clinics, and so forth.
2. Description of the Related Art
A fundus camera disclosed in Japanese Patent Laid-Open No. 5-95902 includes an index for focus indication, a light source that illuminates this index, and a projection optical system that has a split prism for projecting index images onto the fundus of a subject's eye from different positions of the pupil.
In addition, there is also known a method such that a minute prism is provided in an illumination optical system, a slit image illuminated by fundus observation light is projected onto the fundus of an eye, and focus adjustment is performed as disclosed in Japanese Patent Laid-Open No. 6-142050.
In the case of the above-described method, since both a focus index projection lens barrel and a minute mirror that branch from the illumination optical system must be moved in the optical axis direction, a large space is necessary.
In the case of the method in which a minute prism is provided in an illumination optical system, since fundus illumination light is decentered by a prism to project a focus index, the focus index is darker than the surrounding fundus region.
U.S. Pat. Appl. Pub. No. 2006/0077346 proposes an ophthalmic apparatus to solve the above problems, that is, the difficulty of downsizing the apparatus, the problem of increase in cost due to the number of components, adjustment, and so forth, and the problem of light quantity of the focus index. However, in the ophthalmic apparatus of U.S. Pat. Appl. Pub. No. 2006/0077346, a wavelength range different from that of the light illuminating the fundus must be used as an index light source. Specifically, it is necessary to use a near-infrared observation light source and an index light source whose wavelength regions are different from that of a white photographing light source for color photographing. Therefore, the art of U.S. Pat. Appl. Pub. No. 2006/0077346 is limited to non-mydriatic fundus cameras. In addition, the optical axis of the light source for focusing cannot be changed. Therefore, an opening is necessary in the center of a crystalline lens diaphragm, and ghost light can be generated.
As described above, in the conventional arts, the size of the apparatus can be increased or ghost light can be generated.